1. Field of the Invention
This invention relates to an analgesic composition and more particularly to a directly dry compressible composition comprising at least about 70% by dry weight of the composition of acetaminophen and a metal carboxymethyl starch in an amount sufficient for it to function both as a binder and as a disintegrant.
2. Description of the Prior art
Analgesic compositions comprising the active ingredient aspirin are easily tabletted using dry direct compression technologies. Such is not true with compositions having high concentrations of acetaminophen, e.g. in excess of 70 weight percent. Crystalline aspirin is easily tabletted since its crystals are soft and exhibit good plasticity/elasticity when compacted to tablets. Further, cohesive/adhesive bonding within the aspirin tablet is strong and the aspirin itself provides good lubricity to the formula. Accordingly, no lubricant is necessary in the formula used for aspirin tabletting. In contrast, acetaminophen crystals are hard and brittle and fracture very easily. The crystals have essentially no plasticity/elasticity and can be tabletted by the normal aspirin tabletting methods only by using relatively high levels of excipients, typically in excess of 30 weight percent. In addition, largely crystalline grade acetaminophen is sometimes employed to obtain acceptable tabletting, and these large crystals have the disadvantage of being slowly dissolved in the body and require additional tabletting aids to increase the rate of dissolution.
There is a substantial need in the art for a direct tabletting, free flowing, particulate acetaminophen composition which is capable of being directly dry compressed into a tablet having high hardness, short disintegration time and short dissolution time.